IP & subnet math toolbox for DeepSeek Harness

Key features

• Exact arithmetic — IPv4 math uses plain double arithmetic on 32-bit integers (values up to 2³² are exactly representable), so there is no bitwise-overflow risk.
• IPv6 subnet math uses 128-bit BigInt, so every boundary and count is exact
• address counts are returned as decimal strings because they exceed Number.MAX_SAFE_INTEGER.
• /31 follows RFC 3021 — both addresses are reported as usable (point-to-point links).
• /32 is a single host — first/last host equal the address itself.